The present invention relates in general to end controlled walkie/rider pallet trucks commonly used for picking stock in large warehouses and, more particularly, to a coast control arrangement for improved operation of such pallet trucks.
A typical walkie/rider pallet truck includes load carrying forks and a power unit having a steerable wheel, a steering control mechanism, a brake including a deadman brake mechanism, an electric traction motor, a storage battery and a platform onto which the operator may step and ride while controlling the truck. The steering mechanism normally has a handle mounted at the end of a movable steering arm with the handle including controls for raising and lowering the forks and rotatable twist grips or comparable devices to control the speed and direction (forward and reverse) of the truck. A switch for reversing vehicle travel direction when traveling in the power unit first or forward direction and a horn switch are also normally provided on the handle.
In stock picking operations, a truck operator typically follows a winding, unidirectional route through the warehouse, picking up stock in a predetermined sequence in order to maximize productivity. The operator normally walks alongside the truck when the distance along the route between picks is short and steps onto the truck platform to ride when the distance between picks is longer, for example twenty or more feet. When the operator is riding on the truck platform, it is desirable for optimum work productivity to move the truck at higher speeds than when the operator is walking beside it. To this end, speed controllers that include high and low speed control circuits are provided.
For movement of the truck, the operator grasps the handle and moves the steering arm into a truck operating range between a generally vertical (up) braking position and a generally horizontal (down) braking position. If the operator releases the handle, the deadman brake mechanism, for example comprising an arm return spring, forces the arm to the up braking position which actuates a spring-loaded brake to stop the truck. The operator can also actuate the spring-loaded brake by bringing the steering arm to the down braking position. Thus, the walkie/rider pallet truck may be in either a braking or non-braking mode, depending on the position of the steering arm within specified braking and operating arcs.
Rotation of the twist grips controls movement of the truck: rotation of either grip in one direction causes the truck to move with the power unit leading, the forward direction, while rotation in the opposite direction causes the truck to move with the load carrying forks leading, the backward or reverse direction. Increased rotation of the grip in either direction, when operated in either the walkie or the rider mode, results in an increase in the power supplied to the electric motor causing the truck to move at a higher speed in the corresponding forward or reverse direction.
In addition to the motion control provided by the rotatable twist grips, rider pallet trucks may also include side or xe2x80x9cjogxe2x80x9d switches. The jog switches can be turned on and off by an operator walking alongside the truck to move the vehicle at a walk speed of around 3.5 miles per hour (mph) (5.6 km/hr) to move from one stock pick position toward the next stock pick position. A single jog switch is normally provided on each side of the handle either on an outer portion of the handle or, preferably, on an inner, protected portion of the handle. An example of another jog switch arrangement, wherein a pair of switches, one on the outside of the handle and one on the inside of the handle, is provided on each side of the handle and both switches must be activated to move the truck, is illustrated in U.S. Pat. No. 5,245,144 which is entitled WALK ALONG HAND GRIP SWITCH CONTROL FOR PALLET TRUCK which issued on Sep. 14, 1995 to the assignee of the present application and is incorporated herein by reference.
The efficiency of stock picking is severely hampered if the brake is activated every time an operator releases the steering arm. Thus, brake override, or coasting, systems have been developed to override the deadman brake mechanism by preventing the steering arm from entering the up braking position when the operator releases the handle/steering arm while walking alongside the truck. When operating in the coast mode, arrangements are provided for a walking operator to apply the service brake and sound the horn.
One such system for deactivating a deadman brake is disclosed in U.S. Pat. No. 3,791,474 which is entitled MOTION SELECTOR DEVICE FOR A LIFT TRUCK and issued on Feb. 12, 1974 to Crown Controls Corporation, a predecessor in interest to the assignee of the present application. In the ""474 patent, a spring device is manually pivoted into a position for engaging the steering arm and preventing the arm from entering a vertical braking arc under the force of a deadman spring.
Another system for deactivating a deadman brake is disclosed in U.S. Pat. No. 4,716,980 which is entitled CONTROL SYSTEM FOR RIDER VEHICLES and issued on Jan. 5, 1988. In the ""980 patent, a selector switch is used to select either normal high speed operation or coasting operation and additional switches are then used to drive a truck within the high speed range or in the coast mode. Thus, the coasting system of the ""980 patent requires manual engagement of the deadman brake override control device by the vehicle operator to put the truck in its coast mode or to disengage the coast mode for high speed travel.
Another system for automatic engagement and disengagement of a deadman brake is disclosed in U.S. Pat. No. 5,964,313 which is entitled MOTION CONTROL SYSTEM FOR MATERIALS HANDLING VEHICLE and issued on Oct. 12, 1999. In the ""313 patent, a coast control device can only be engaged by activation of a jog button that actuates a low speed travel mode. The coast control device is deactivated by activation of a maximum speed control button or movement of speed control hand grips from their neutral position. The coast control device comprises a coast control spring that is compressed by a solenoid to apply a coast spring force that compensates the force provided by a handle return spring to constrain the steering arm to a driving arc. While the automatic engagement and disengagement of coast control improves on operation of the truck during stock picking, the disclosed coast control mechanism is mechanically complicated and, when engaged and the handle is released, forces the handle into a single detent-defined position within the driving arc. Further, since the coast control device can only be engaged by activation of the jog button, the ""313 coast control cannot be used on vehicles that do not have the jog feature.
Accordingly, there is a need for a mechanically less complicated coast control arrangement for walkie/rider pallet trucks that would have less parts, be easier to assemble and maintain, and enable an operator to retain the handle at any position within the operating arc, allow the coast system to be overridden for applying the brake, allow coast to be used on walkie/rider pallet trucks that do not have the jog feature, limit truck speed to approximately 3.5 mph (5.6 km/hr) when the coast mode is selected, and provide improved operation of the truck for stock picking.
This need is met by the invention of the present application wherein a device locks the position of a steering arm of a walkie/rider pallet truck to prevent movement of the steering arm by a deadman mechanism that would otherwise move the steering arm into a generally vertical truck braking position. By locking the position of the steering arm to overcome the deadman mechanism, the truck is placed into a coast mode of operation. The currently preferred locking device is a steering arm brake comprising an armature plate mounted to and movable with the steering arm and an electromagnet coupled to a steering head to which the steering arm is movably mounted so that the armature plate moves over the electromagnet. The coast mode of truck operation is activated by operating the electromagnet to attract the armature plate and thereby lock the steering arm into the position it occupies when the coast mode is activated. While the braking force locks the steering arm and prevents movement of the steering arm by the deadman mechanism, the force can be overcome by the truck operator to manually apply the truck brake or to reposition the steering arm to a new position where it is again locked until it is once again moved to a new position, the truck is braked or the coast mode is released.
The invention of the present application also provides novel control for coasting operation of a walkie/rider pallet truck. A coast control mechanism for overriding a deadman brake to enable coasting operation of a walkie/rider pallet truck is manually engaged by an actuator or coast switch that is mounted on or closely adjacent to a grab bar that is provided on the truck and is to be gripped by an operator riding on the truck. The actuator can be on the grab bar, on a control panel mounted on the grab bar or mounted to be easily accessible by an operator""s hand gripping the grab bar for operation of the truck and coast actuation. Coasting operation of the truck is cancelled by manually operating a high speed/coast release switch.
Additional features and advantages of the invention will be apparent from the following description, the appended claims and the accompanying drawings.